Characters
Upon completion of all events per stage, you will unlock a corresponding player. They are:

Alex Kidd - Alex Kidd stage
Amy Rose - Sonic the Hedgehog stage
Gilius Thunderhead - Golden Axe stage
Gum - Jet Grind Radio stage
MeeMee - Super Monkey Ball stage
Pudding - Space Channel 5 stage
Reala - NiGHTS stage
Shadow the Hedgehog - Sonic the Hedgehog stage